A VCO is an electronic oscillator designed to be controlled in oscillation frequency by a voltage input. The frequency of oscillation is varied by applied direct current (DC) voltage, while modulating signals may also be fed into the VCO to cause frequency modulation (FM) or phase modulation (PM). VCOs are used in virtually all Spread Spectrum, radio frequency (RF), and wireless systems.
However, IC fabrication process variation is a factor that may limit the designable frequency-range of VCOs. For example, in advanced complimentary metal-oxide-semiconductor (CMOS) technologies, wide variation in CMOS fabricating processes (e.g., lithographic processes) that influence the features of the CMOS structures (e.g., lengths, widths, oxide thicknesses, etc.) necessitates innovative circuit designs to counteract the process variation.
Accordingly, there exists a need in the art to overcome the deficiencies and limitations described hereinabove.